1. Field of Invention
The invention relates to use of coal fly ash in the growth and harvesting of turfgrasses.
2. Description of the Related Art
The use of coal to produce electric power or steam requires large quantities of coal annually. In the U.S., coal is the most extensively used and most important source of energy, and will most likely continue to be so for the foreseeable future. The combustion of coal results in the production of vast quantities of coal combustion by-products (CCBPs) which must be disposed. CCBPs are classified into three general types of ash: fly ash, bottom ash and boiler slag. Currently, the most widely accepted disposal practices are landfilling and storage in settling ponds. Only about 25% of the solid residues from coal combustion, i.e. fly-ash and bottom ash, is utilized. Main uses include partial substitution in cement mixes, structural fills, and road base. The low usage ensures that vast amounts of CCBPs are accumulating in disposal facilities, unutilized.
The expense associated with disposal is ever increasing. The expense is primarily associated with the escalating cost of constructing new state-of-the-art landfills. About 70% of power generating facilities utilize landfilling and impoundments as disposal techniques, due to the limited utilization of CCBPs. Thus, there is an incentive to explore other uses of coal fly ash to reduce or eliminate the cost of disposal.
Due to the rather low usage of CCBPs, research is now addressing new usage options which could utilize a greater percentage of the total material produced. Large scale application on lands has been proposed as a promising utilization option. For example, fly-ash has been demonstrated effective in reclaiming acid mine spoils. Because of the liming potential of certain fly-ashes and their ability to provide essential nutrients for plant nutrition, CCBPs are being considered for amending agricultural soils to improve both chemical and physical properties. However, the quantities of CCBPs utilized in mine spoil reclamation can far exceed those suitable for cropland application. Reported benefits of adding fly-ash to problem soils include: enhanced texture for coarse and fine textured soils, improved water holding capacity, and increased pH in acidic soils. Because of the dominance of silt-size particles in fly-ash, this material may often be substituted for topsoil in surface mine lands, thereby enhancing the physical conditions of the soil, especially the water holding capacity.
Application of CCBPs to agricultural lands has both advantages and disadvantages. For example, application of certain fly ashes can increase pH. However, the pH enhancement caused by alkaline fly-ash may cause plant nutrient imbalance, particularly P deficiency and antagonistic reactions among elements because of excessive Ca, K, and S. On the other hand, certain fly-ashes with some unburned coal could produce acidic constituents through the oxidation of pyrite (i.e., FeS.sub.2). This oxidation serves to lower soil pH and facilitate the solubility of many trace elements. The solubility of salts in fly-ash particles may cause salinity problems in soils resulting in increases of electrical conductivity in soils, which may retard plant growth, especially in semi-arid and arid conditions. The net effect of fly-ash in soil due to changes in soil pH, salinity, and trace element concentrations could affect both the plant and soil chemical characteristics.
Excessive application rates can result in phytotoxic levels of B, and elevated levels of As, Mo, and Se in plant tissues. Nevertheless, B accumulation in corn (Zea mays) as supplied by additions of fly-ash and flue gas desulfurization (FGD) have been reported. Of greatest concern in the long-term usage of fly-ash is the lingering effect of especially Mo and Se and their eventual bioaccumulation in plant tissues. While these elements do not generally produce detrimental effects in plant growth, they are of great concern in animal nutrition as their safe range is very narrow. Because of the potential tainting of the food chain by such trace elements as Mo and Se in the form of feedstuff grown on fly-ash amended soils, the possibility of risk to livestock health should be embodied in the long-range planning for agricultural production purposes.
Some soil physical and related properties have been enhanced by the use of CCBPs with a concomitant increase in aeration and reduced bulk density from the application of silt-sized CCBPs. Although enhancement of water holding capacity of some soils has been reported due to CCBPs application, it continues to be unclear whether this beneficial effect translates directly into increased available water for plant use. In a recent field study, however, banding of ash into the soil at a 45-degree angle to the surface produced increases in corn yield, apparently due to the increased water holding capacity with ash-banded soils. In applying large quantities of CCBP, special consideration should also be given to potential effects on groundwater quality.
Due to the fact that the application of certain fly-ashes, especially at high rates, can potentially affect the quality of the plant material, including crops, other innovative applications need to be explored.
Application of CCBPs generally is regulated by individual states under solid waste regulations developed within the guidelines of the Resource Conservation and Recovery Act (RCRA) of 1976. These regulations vary from very stringent to total exemption from regulation for onsite disposal. For example, in the state of South Carolina, the CCBPs regulation comes under "Solid Waste Management: Land Application of Solid Waste" promulgated in 1996 (SCDHEC, 1996). This regulation addresses the land application of non-hazardous solid waste on, or into, land that is managed to produce crops or forest products and to applications of solid waste on land that is being reclaimed to enhance its aesthetic value or reduce environmental degradation. Further, the land application of non-hazardous solid waste shall be for beneficial agricultural, silvicultural, and horticultural purposes and not used as a means of disposal. The CCBP use falls under "Class I Solid Waste" that refers to those solid wastes, which have the potential to add some nutrient and/or pH adjustment benefit to the soil. These regulations must adhere to all federal, state, and local zoning, land use and other applicable ordinances, regulations, and laws. An important provision of the SCDHEC regulation deals with ceilings for cumulative lifetime loads of the following eight metals: As=41, Cd=39, Cu=1,500, Pb=300, Hg=17, Ni=420, Se=100, and Zn=2,800 kg ha.sup.-1.
There are a number of U.S. patents which propose use of coal products for soil conditioning. U.S. Pat. No. 4,985,065 discloses a soil conditioner mainly for improving water retention which includes coal ash.
U.S. Pat. No. 5,013,349 discloses a soil conditioner which employs coal ash as a filler.
U.S. Pat. No. 3,900,378 provides an insoluble swellable polymer comprised of a mixture of a hydrogel and an inert filler which can be coal dust. The mixture can be used as a soil amendment.
U.S. Pat. Nos. 5,248,327 and 4,541,857 disclose soil conditioners using coal-derived products, such as humic acid or a particulate coal.
A coal ash fertilizer composition is disclosed in U.S. Pat. No. 4,469,503.
Although some of the above patents disclose use of coal or coal ash, the amounts of coal ash utilized is relatively low, and other components are required which increases the cost of the soil conditioners.
There remains a need to find suitable and innovative uses of CCBPs which are relatively inexpensive, and which can meet current government regulations.